1. Field of the Invention
This invention relates to a video signal processing apparatus and a video signal processing method adapted to encode moving pictures and efficiently switch resolution and therefore the number of pixels within an image sequence.
2. Description of the Related Background Art
MPEG2 (Moving Picture Experts Group Phase 2) represents a coding system designed for applications including broadcasting and AV equipment and being popularly used as technique for compressing information in the form of pictures, sounds and data.
MPEG2 encodes input data such as video data and audio data as well as other data on the basis of bit rate. As for pictures, it divides a picture into mxc3x97n blocks and transforms them by means of orthogonal functions to concentratively exploit the signal power and compress the entire volume of information.
Image data encoded by MPEG2 shows a hierarchical structure extending from a sequence layer down to a block layer.
To be more accurate, a bit stream conforming to the MPEG2 Standards comprises a sequence layer of a group of serially arranged pictures having common attributes, a GOP (group of pictures) layer operating as the smallest unit for a group of pictures adapted to be randomly accessed, a picture layer of common attributes of a picture, a slice layer for information common to small pictures obtained by slicing the screen, a macro-block layer for information common to pixel blocks (macro-blocks) obtained by further dividing the slice layer and a block layer for transform coefficients per se.
The picture layer deals with pictures according to a main level format. In the case of NTSC television signals, for example, a picture is expressed by 704 (H)xc3x97480 (V) pixels.
Pictures are categorized as I pictures or intra-coded pictures, P pictures or predictive-coded pictures that are forwardly predictive-coded pictures and B pictures or bidirectionally predictive-coded pictures that are forwardly and backwardly predictive-coded pictures. The GOP layer comprises a plurality of pictures.
For processing moving pictures according to MPEG2, however, input pictures are coded and then the information generated therefrom is observed over the entire sequence to determine the characteristic aspects of the series of input pictures, which are then used to control the encoding operation and improve the quality of the pictures obtained after the encoding/decoding process.
However, this technique is useless in a real time system where pictures that are arbitrarily input typically by means of a movie digital camera are subjected to a compressed coding process and a rewriting process conducted on a recording medium on a real time basis.
In such a system, it is necessary that a series of moving pictures are compression coded to reflect at least some of the characteristics of the series of pictures in a single real time coding operation.
In view of the above identified problem, it is therefore the object of the invention to provide a video signal processing apparatus and a video signal processing method that can perform a coding operation to reflect the characteristics of a series of moving pictures in a single real time coding process for a system that is required to operate on a real time basis.
According to an aspect of the invention, the above object is achieved by providing a video signal processing apparatus adapted to encode video signals of pictures on a basis of group of a plurality of pictures, characterized by comprising:
input means for receiving input video signals;
specification means for specifying the resolution of said input video signals;
control means for controlling the number of pictures of two temporally adjacent groups of pictures containing a changing point of said specified resolution of video signals to be maintained to a constant value; and
coding means for coding said two groups of pictures.
According to another aspect of the invention, there is provided a video signal processing method for encoding video signals of pictures on a basis of group of a plurality of pictures, characterized by comprising steps of:
specifying the resolution of input video signals;
controlling the number of pictures of two temporally adjacent groups of pictures containing a changing point of said specified resolution of video signals to be maintained to a constant value; and
coding said two groups of pictures.
According to still another aspect of the invention, there is provided a video signal processing apparatus adapted to encode video signals of pictures on a basis of group of a plurality of pictures, characterized by comprising:
input means for receiving input video signals;
specification means for specifying the resolution of said input video signals;
control means for dividing said pictures into a plurality of regions, weighting each of said regions by the degree of coding difficulty and switching resolution for each group of pictures according to said weighted degree of coding difficulty; and
coding means for coding said two groups of pictures.
According to still another aspect of the invention, there is provided a video signal processing method for encoding video signals of pictures on a basis of group of a plurality of pictures, characterized by comprising steps of:
specifying the resolution of input video signals;
dividing said pictures into a plurality of regions, weighting each of said regions by the degree of coding difficulty and switching resolution for each group of pictures according to said weighted degree of coding difficulty; and
coding said two groups of pictures according to said resolution.
Thus, when compression coding moving pictures input to a video camera according to the invention, temporally adjacent two GOPs containing a changing point of resolution are made to show a constant number of frames, e.g., 30 frames, so that the bit rate is held substantially to a fixed level within the two GOPs (=30 frames). As a result, a video signal processing apparatus and a video signal processing method according to the invention can easily be applied to a recording/reproducing apparatus using disks for recording/reproducing video signals at a fixed bit rate.
Additionally, when compression coding moving pictures input to a video camera according to the invention, each frame is divided into a number of areas, each of which is weighted by the degree of coding difficulty and the resolution of the input pictures is switched on the basis of the BD values of the weighted areas. Thus, a fixed state of the camera is predicted by taking the fluctuations of the BD values and the values of motion vectors that a sufficiently small in four corners of the screen into consideration. As a result, any local bias of the degree of coding difficulty within the screen can be corrected to switch resolution effectively and efficiently.